JPH0363614A - Zoom lens - Google Patents

Abstract

PURPOSE:To obtain the lightweight, compact lens which provides high-speed power zooming by serving one of moving lens groups also as focusing and satisfying specific conditions. CONSTITUTION:The lens system is constituted of a 1st lens group I with positive refracting power, a 2nd lens group II with negative refracting power, a 3rd lens group III with positive refracting power, and a 4th lens group IV with a negative refractive index, and the 1st lens group I is served also as focusing. Then other moving lens groups are moved linearly so that expressions I are satisfied. Here, Xf is the quantity of movement of the lens group which moves most to the object side from the wide-angle end corresponding to optical focal length (f) at the time of zooming from the wide-angle end to the telephoto end and Yf is the quantity of movement of other lens groups which are not served as focusing from the wide-angle end corresponding to the focal length (f).

Description

[Detailed description of the invention] Regarding.

Usually, each lens group of a zoom lens is driven by a cam. However, if a zoom lens using a cam is driven by a motor in order to achieve power zoom, a large torque is required, resulting in an increase in the size of the drive unit and a decrease in zooming speed.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and provide a lightweight, compact zoom lens suitable for high-speed power zooming.

In order to achieve the above object, the zoom lens according to the present invention has three or more moving lens groups during zooming, one of these moving lens groups is also used for focusing, and all other moving lens groups meet the following conditions. It is characterized by linearly moving each other in the entire zooming range to satisfy the following: (1) −1,5<a≦, where X is the zooming from the wide-angle end to the telephoto end of the linearly moving lens group. Y is the amount of movement from the wide-angle end at a given focal length f of the lens group that moves the most toward the object side during focusing; Amount of movement: For both X and Y, movement in the image plane direction is positive, and movement in the object direction is negative.

As described above, in this invention, all lens groups other than the lens group used for focusing are linearly moved relative to each other in the entire zooming range in a manner that satisfies condition (1).
The drive can be performed by a feed screw instead of a cam. In this case, the moving speed ratio of each lens group is determined by the pitch of the feed screw, and the pitch is constant over the entire zooming range. As described above, in the present invention, the lens is driven by a simple, lightweight and compact mechanism using a feed screw.

Furthermore, since the drive torque can be reduced, the drive system can be made more compact and the drive speed can be increased.

On the other hand, the lens group that is also used for 7 focussing is driven not by a cam but by a screw, and its control is performed by automatically rotating the screw in a direction that eliminates out-of-focus based on focus detection by a focus detection device. Focus deviations occur due to the movement of the subject or the movement of the linearly moving lens group due to power zoom, but in either case, the focus deviation is corrected by moving the lens group that is also used for focusing, and as a result, the image plane position remains constant. is maintained.

Condition (1) is the state where the total length is the shortest (wide-angle end)
This is a condition for shortening the total length at , and realizing the desired linear movement for the entire linearly moving lens group. conditions(
The lower limit of 1) is for the case where Yf is positive (movement toward the image plane side), and is intended to keep the amount of movement within 1x, 1.5 times 1. If the lower limit is exceeded, the air gap required for zooming must be increased, resulting in an increase in overall length.

The upper limit is when Y is negative (movement toward the object), and the amount of movement
This is a case where the lens group of , and the lens group of movement amount Yl move in the same direction.

α = 1 when the lens group that moves Yl is linked to the lens group that moves X and moves together, and another lens group is interposed between these lens groups. Applicable. When there is no other lens group between both lens groups, a-1 means that both lens groups can no longer be called two lens groups, but act as one lens group as a whole. Such a case does not exist.

Further, in the zoom lens according to the present invention, in order from the object side power, a first lens group having a positive refractive power, a negative additive power, and a second lens group having a negative refractive power.
It consists of a lens group, a third lens group with positive refractive power, and a fourth lens group with negative refractive power, of which the - group is used for both zooming and focusing, and one of the groups is used for the entire zooming area. It is desirable to move them linearly with respect to each other.

Furthermore, the zoom lens according to the present invention has at least the first lens group and the second lens group when zooming from the wide-angle end to the telephoto end.
It is desirable that the distance between the third lens group and the fourth lens group is increased, the distance between the third lens group and the fourth lens group is decreased, and the following conditions are satisfied.

however, φl is the refractive power of the first lens group, φ2 is the refractive power of the second lens group, φ3 is the refractive power of the third lens group, φ4 is the refractive power of the fourth lens group.

Exceeding the upper limit of condition (2) is disadvantageous because the amount of relative movement between the first lens group and the second lens group necessary to ensure a sufficient zoom ratio increases. Moreover, if the lower limit is exceeded, the lens diameter of the third lens group becomes large, which is disadvantageous for making the diameter compact.

If the upper limit of condition (3) is exceeded, it becomes difficult to secure sufficient back focus. In addition, if the lower limit is exceeded, the third lens group and fourth lens group necessary to ensure a sufficient zoom ratio
This is disadvantageous because the amount of relative movement of the lens groups becomes large.

Exceeding the upper limit of condition (4) is disadvantageous because the amount of relative movement of the third and fourth lens groups necessary to ensure a sufficient zoom ratio increases. Moreover, when the lower limit is exceeded, the refractive power arrangement of the telephoto type becomes excessive, and positive distortion increases overall, and especially distortion near the telephoto end becomes unacceptable.

Note that when such a zoom type is used, it is desirable that the following is satisfied, where the value of Y of the lens group whose absolute value of the movement amount is the smallest is Y,min. When the lower limit of condition (5) is exceeded, a larger air gap is required for zooming at the wide-angle end, and the overall length becomes longer.

Further, in the zoom lens according to the present invention, it is desirable that the first lens group be used for both zooming and focusing. In this case, the amount of movement of the second, WI3, and fourth groups from the wide-angle end to the telephoto end is X, respectively, with the image plane direction being positive.
X3. When expressed as X, it is desirable to satisfy the condition.

Condition (6) defines the ratio of the amount of movement of the second lens group to the fourth lens group, and condition (7) defines the ratio of the amount of movement of the third lens group to the fourth lens group. Conditions (6), (7)
Both of these are conditions for appropriately balancing the total lens length at the wide-angle end, where the total lens length is the shortest, and the amount of movement of the first lens group associated with zooming. If condition (6) or condition (7)
), the total length of the lens at the wide-angle end will be shortened, but the amount of movement of the first lens group due to zooming will become large, making it difficult to configure the lens barrel. Furthermore, if the lower limit of condition (6) or (7) is exceeded, the amount of movement of the first lens group associated with zooming becomes small, which is advantageous in terms of the structure of the lens barrel;
The total length of the lens at the wide-angle end becomes long, making it impossible to obtain a compact zoom lens.

By the way, in the zoom lens according to the present invention, when zooming is performed in a focused state at infinity, the 7 focusing lens groups move nonlinearly with respect to the other linear moving lens groups.

Therefore, in order to maintain a focused state even when zooming, a mechanism for imparting nonlinear movement to the focusing lens group is required. However, using a cam as before is contrary to the purpose of the present invention and is not appropriate. on the other hand,
Many cameras these days have built-in automatic focus adjustment mechanisms that automatically drive the lens group in a direction that eliminates out-of-focus based on the focus detection by the focus detection device, and the adjustment speed has become faster, making zooming easier. It is fully possible to simultaneously perform automatic focus adjustment and control the position of the focusing lens group. Taking these circumstances into consideration, when actually using the zoom lens according to the present invention, it can be considered that an automatic focusing mechanism can be used in place of a mechanism that nonlinearly moves the focusing lens group.

Therefore, it is desirable that the zoom lens according to the present invention satisfy the following conditions.

Here, SL and S are the unit movement amount of the linear movable lens group that moves the largest toward the object side and the relative movement amount of the focusing lens group when zooming is performed in the infinity focused state, respectively, lsp/SL1w is the ratio of S and SL at the wide-angle end, l
sp/5tlt is the ratio of S and SL at the telephoto end.

Condition (8) is intended to provide a configuration suitable for controlling the position of the seven focusing lens groups during zooming using the automatic focal length adjustment mechanism.

Generally, in a zoom lens, the depth of field is shallower at the telephoto end than at the wide-angle end, so higher positional accuracy of the focusing lens group is required at the telephoto end. Therefore, when performing zooming--4 and simultaneously operating the automatic focusing mechanism to control the position of the focusing lens group 7,
As shown in condition (8), if the configuration is such that the amount of movement of the focusing lens group relative to the unit movement amount of the linear moving lens group becomes smaller toward the telephoto side, when zooming is performed at the telephoto side, focusing Since the amount of positional correction of the lens group can be small, it is easier to obtain high accuracy. Conversely, contrary to condition (8), if the moving amount of the focusing lens group relative to the unit moving amount of the linearly movable lens group is configured to increase toward the telephoto side, when zooming is performed at the telephoto side, 7 The amount of position correction of the excusing lens group becomes large, resulting in a decrease in accuracy and an increase in control time.

Furthermore, in order to increase the zoom magnification, it is desirable that at least one of the second lens group and the third lens group moves. Furthermore, when zooming from the wide-angle side to the telephoto side, it is desirable that the distance between the second lens group and the third lens group be reduced.

table (Example 1) below, Examples 1 to 7 of the present invention are shown in Tables 1 to 7, respectively.

Here, : Focal length of the entire system, : Open F number r i (i = 1.2.3...): 1st from the object side
Radius of curvature of the th lens surface, d i (i= 1.2.3...): 1st from the object side
th axial spacing, N i (i-1, 2, 3...): Refractive index of the first lens from the object side for the d-line, νi (i= 1.2-3...): The Atsube number of the first lens from the object side is:

Table 8 shows the relationship between each example and each condition (2) to (7).

f-suit5 ~ 140.0 ~ 195.0 F-4, 6 ~ 5.5 ~ 5.8 dll skewer radius axis upper surface spacing refractive index (Nd) Atsube number (νd) Amount of movement of the 4th lens group is , then Y, : The amount of movement of the second lens group is Y, : The amount of movement of the third lens group is σ-〇α-o, 5 Now, the amount of movement of the fourth lens group is SL, and the amount of movement of the first lens group is SL. Table 2 (Example 2) with the amount of movement as SP f-82,5~140.0~195.0 Blood rate Radius axis upper surface interval F-4,6~5.5~8 Refractive index (Nd) Atsube number (νd) Table 3 (Example 3) f-1015~14 (LO~195.0 Radius of curvature axis upper surface distance F-4,6 Refractive index (Nd) Atsube number (νd) Amount of movement of the 4th lens group is XI Let Yl: the amount of movement of the second lens group, then Yl: let the amount of movement of the third lens group be m, then α--0,23 α-0,53 Let the amount of movement of the fourth lens group be X, then Y,: the second The amount of movement of the lens group is Y, and the amount of movement iJI of the second and third lens groups is mini-1,1.
3 aself 0 Table 4 (Example 4) Table 5 (Example 5) f-I 5 ~ 140.0 ~ 195.0 where the amount of movement of the fourth lens group is SL and the amount of movement of the first lens group is Sr Curvature radius pongee top surface spacing F-4, 6 to 5.5 to 5.8 Bent skewer (Nd) Atsube number (νd) f-25 to 140.0 to 195.0 Curvature radius sleeve top surface spacing F trout 4.6 Refractive index (Nd) Atsube number (shid) If the amount of movement of the fourth lens group is X, and Yl is the amount of movement of the second lens group, then α-0,31Y
l: the amount of movement of the third lens group, then a-0,64 4th
If the amount of movement of the lens group is Xl and Y is the amount of movement of the second lens group, then α--1,11
Y: If the amount of movement of the third lens group is α--0,16
Table 6 (Example 6) f-8L5-140.0 -195.0 Radius of curvature Ring top surface distance F-4,6~ &5~5.8 Refractive index (Nd) Atsube number (νd) Table 7 (Example 7) f-Fin, 0-50.0-62-0 Radius of curvature◆-Top distance F-4,5~5.5 ~5.8 Refractive index (Nd) Atsube number (νd) Yl: α-0,5 as the amount of movement of the third lens group Y,: a-0,77 as the amount of movement of the first lens group 1.3.5.7.9.11.13 are lens sectional views showing the arrangement of each lens group at the wide-angle end and movement to the telephoto end in Examples 1 to 7 of the present invention, respectively. However, here, (I) is the first lens group, (■) is the second lens group, (■) is the third lens group, and (IV) is the fourth lens group. The straight line and curved line below the lens group indicate the movement of the lens group,
The dotted line indicates that the lens group does not move.

Figures 2.4.6.8.10.12.14 show the wide-angle end S〉 and intermediate focal length condition <M of Examples 1 to 7 of the present invention, respectively.
2 is an aberration diagram showing each aberration at the telephoto end (L>) and the telephoto end (L>). Here, F is the open F number and Y' is the image height.

FIG. 15 is a sectional view showing a feed screw and an automatic focusing mechanism for moving each lens group of the zoom lens according to the present invention. 8 in FIG. 15, the first lens (Ll), the second lens
Lenses (L, 3rd lens (L, ) and 4th lens (L)
The lens movements in 4) are the first lens group (■) and the second lens group (■) of the zoom lens according to Example 1 shown in FIG.
This corresponds to lens movement of the third lens group 1), the third lens group 1), and the fourth lens group. In other words, the first lens (Ll) is used for both zooming and 7 focusing, and the third lens (L,) and the fourth lens
The lenses (L,) move linearly with respect to each other.

Here, the second lens (L2) does not move.

To linearly move the third lens (L,) and fourth lens (L,) for zooming, first move the zoom motor (
ZM) rotates, and the gear (6) and zoom gear barrel (5) rotate accordingly. When the gear (7) and the feed screw (8) rotate due to the rotation of the zoom gear cylinder (5), the gear (9) and the feed screw (1) are rotated by the feed screw (8).
0) rotates, the lens holding frame (4) screwed to the feed screw (10), that is, the fourth lens (L,) moves back and forth on the optical axis. At this time, the lens movement speed ratio of the third lens (L,) and the fourth lens (L4) is determined by the pitch of the feed screws (8) and (10) or the number of teeth of the gears (7) and (9). can be a value that is constant over the entire range of zooming.

On the other hand, the first lens (Ll) which is also used for focusing
is for the third lens (L,) and the fourth lens (L,),
Although it moves nonlinearly, it is driven by a screw and controlled by an automatic focus adjustment mechanism. Specifically, the focus detection device (P
Day 7 using TTL light after zooming at T)
The microcomputer (CPU) detects the amount of orcus.
When inputting, the microcomputer (C: P U)
calculates the motor rotation amount corresponding to the input day focus amount and inputs it to the motor control circuit (MC). The motor control circuit (MC) drives the focus motor (FM) based on the input motor rotation amount,
Along with this, the gear (12) rotates. Lens holding frame (
2) is screwed to the fixed lens barrel (1), and the gear (12
) and is rotated by a 7 orcus motor (FM) to move back and forth on the optical axis. Therefore, the first lens (Ll
) also moves back and forth on the optical axis. Here, the focus detection device (D
T), a microcomputer (CPU), a motor control circuit (MC), and a focus motor (FM) work together as an automatic focus adjustment mechanism. Note that in FIG. 15, CM) indicates a mirror for focus detection.

Note that even if a movable or fixed lens group with a simple configuration and a weak refractive power is placed between any group of the zoom lens according to the present invention or on the object side or image side of the entire system, it will not work. It has the same purpose, means, and effect as the present invention, does not deviate from the idea of the present invention, and is included in the present invention.

[Brief explanation of drawings]

1.3.5.7, 9.11.13 are lens sectional views showing the arrangement of each lens group at the wide-angle end and movement to the telephoto end in Examples 1 to 7 of the present invention, respectively; 6.8.
10.12.14 are aberration diagrams showing aberrations at the wide-angle end, intermediate focal length state, and telephoto end of Examples 1 to 7 of the present invention, respectively, and Fig. 15 shows each group of the zoom lens according to Example 1 of the present invention. FIG. 3 is a cross-sectional view showing a driven feed screw and an automatic focus adjustment mechanism. (1) (n) (II[) (IV) : 1st lens group, : 2nd lens group, : 3rd lens group, : 4th lens group.

Claims (1)

[Claims] (1) In a zoom lens in which three or more groups move during zooming, one of these moving lens groups is also used for focusing, and all other moving lens groups satisfy the following conditions. A zoom lens characterized by linearly moving each other in the entire zooming range as follows: -1.5<α≦1 α=Y_f/X_f=constant, X_f<0 where X_f is the wide-angle lens of the linearly moving lens group. Y_f is the amount of movement from the wide-angle end at a given focal length f of the lens group that moves most toward the object side during zooming from the end to the telephoto end; This is the amount of movement from the wide-angle end. (2) a first lens group having positive refractive power in order from the object side;
The second lens group has negative refractive power, and the third lens group has positive refractive power.
A patent comprising a lens group and a fourth lens group having negative refractive power, one of which is used for both zooming and focusing, and at least the other two groups are moved linearly relative to each other over the entire zooming range. A zoom lens according to claim 1. (3) When zooming from the wide-angle end to the telephoto end, the distance between at least the first lens group and the second lens group increases,
A zoom lens according to claim 2, characterized in that the distance between the third lens group and the fourth lens group is reduced and the following conditions are satisfied: -3.5<φ_2/φ_1<-0 .8 1.5<φ_3/φ_1<4.0 -4.0<φ_4/φ_1<-1.2 However, φ1 is the refractive power of the first lens group, φ2 is the refractive power of the second lens group, and φ3 is the refractive power of the second lens group. The refractive power of the third lens group, φ4, is the refractive power of the fourth lens group. (4) A zoom lens according to claim 3, characterized in that it further satisfies the following conditions: -0.7<Y
_fmin/X_f≦1 However, Y_fmin is Y_ of the lens group with the smallest absolute value of movement amount.
is the value of f. (5) A zoom lens according to claim 2, wherein the first lens group is used for both zooming and focusing. (6) A zoom lens according to claim 5, which satisfies the following conditions: -1.5<X_2/X_4<0.5 -0.4<X_3/_X_4<0.9 , X_4<0 However, X_2, X_3, and X_4 are the amounts of movement of the second, third, and fourth lens groups from the wide-angle end to the telephoto end, respectively. (7) The zoom lens according to claim 1, wherein the lens group used for focusing is automatically driven in a direction to eliminate out-of-focus based on focus detection by a focus detection device.